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Eclogite relics in the Variscan orogenic belt of Bulgaria (SE Europe)

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Abstract

Eclogitic rocks were sampled from two zones in the basement of the Sredna Gora terrane (central western Bulgaria): (1) partially retrogressed eclogites and amphibolites embedded in sillimanite-bearing garnet-micaschists with kyanite relics and migmatites and (2) banded amphibolites associated with muscovite-bearing metagranites within two-mica paragneisses. Rutile relics and oligoclase + green hornblende + epidote ± biotite pseudomorphs after garnet suggest an eclogite facies event. A tholeiitic, transitional affinity was determined for the protoliths, suggesting a continental rift environment, consistent with several eclogite-bearing complexes in the eastern segments of the Variscan belt that arose from the Cambro-Ordovician Gondwana break-up. Decreasing pressure after the eclogite overprint was demonstrated by (a) diopside-albite symplectite, and (b) plagioclase + red–brown to green amphibole kelyphite. The early static re-equilibration, dated to 398 ± 5.2 Ma by 40Ar–39Ar technique, was followed by an amphibolite facies foliation, which was pervasive in amphibolites, gneisses and micaschists, and poorly developed in eclogites. The lithospheric PT paths corresponding to higher and lower metamorphic gradients reflect the juxtaposition of crustal and lithospheric mantle units, respectively. In the build-up of the basement of the Balkan orogen, the physical properties of the lithological complexes might have influenced the collisional pattern of involved microplates.

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Acknowledgments

This research was carried out within the bilateral CNR (Italy)–BAN (Bulgaria) project. The reviews by F.M. Brouwer, Ingo Braun and an anonymous referee helped us to improve the early versions of the manuscript.

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Authors and Affiliations

  1. Department for the Study of the Territory and its Resources, University of Genoa, Corso Europa 26, 16132, Genoa, Italy

    Laura Gaggero, Laura Buzzi & Luciano Cortesogno

  2. Geological Institute of the Bulgarian Academy of Sciences, Acad. Georgi Bontchev, Str. Block 24, 1113, Sofia, Bulgaria

    Ivan Haydoutov

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  1. Laura Gaggero
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  2. Laura Buzzi
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  3. Ivan Haydoutov
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  4. Luciano Cortesogno
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Correspondence to Laura Gaggero.

Additional information

Luciano Cortesogno is deceased.

Mineral abbreviations are after Kretz (1983).

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Gaggero, L., Buzzi, L., Haydoutov, I. et al. Eclogite relics in the Variscan orogenic belt of Bulgaria (SE Europe). Int J Earth Sci (Geol Rundsch) 98, 1853–1877 (2009). https://doi.org/10.1007/s00531-008-0352-x

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